This invention relates generally to improvements in prosthetic joints, such as knee joints and the like. More particularly, this invention relates to an improved joint prosthesis designed for enhanced fixation by means of direct ingrowth of bone and other living tissue, thereby avoiding use of fixating bone cements and the like.
Artificial or prosthetic joint mechanisms for implantation into animals, particularly humans, have been the subject of intensive research and development efforts for many years. Such prosthetic joint mechanisms have typically comprised one or more implant components formed from a relatively biostable material of selected structural properties and uniquely shaped to replace all or part of a selected anatomical joint, for example, a hip or knee joint. The implant components are installed by surgically accessing the joint and by resection of one or more bone surfaces to accommodate direct attachment thereto of the implant components. In the past, this bone attachment has been commonly achieved by use of bone cements, such as a methyl methacrylate-based cement or the like used as a grouting material to fill up the space between the receptive bone surface and the prosthetic component. In the process of its application, the cement interdigitates within the interstices of the bone surfaces to achieve mechanical fixation at the bone cement interface.
In recent years, a variety of potential disadvantages or limitations have bee recognized with respect to cemented fixation of prosthetic joint mechanisms. More particularly, it is generally recognized that the use of bone cement to fixate prosthetic joint implant components provides a temporary securement which normally requires significant restrictions upon later patient activity to avoid failure of the cemented interface during the patient's lifetime. Failure of the cemented interface is especially undesirable, since the bone cement contributes to a significant degree of localized loss of bone structure which makes implantation of a secondary prosthesis extremely difficult and frequently impossible. These problems encountered by use of cemented prosthetic mechanisms are particularly severe with high load bearing, highly stressed joints, such as the knee joint.
In an effort to avoid use of bone cements, a variety of improved prosthetic joint mechanisms have been proposed for noncemented attachment to resected bone surfaces. Some of these noncemented mechanisms have envisioned enhanced mechanical attachments to the bone by means of press-fitted anchoring pegs and the like. Alternatively, other proposed joint mechanisms have suggested the use of attachment surfaces having closely controlled porosity characteristics designed for accommodating direct bone attachment by ingrowth of living cancellous bone or tissue. However, while these bone ingrowth proposals appear to offer significant advantages over previous cement fixated designs, the load-bearing capacity of ingrowth fixated prostheses has been limited, thereby preventing their widespread use at highly loaded and stressed joints, such as the knee, without requiring significant restrictions on subsequent patient activity to minimize risk of failure of the bone ingrowth interface.
There exists, therefore, a significant need for an improved joint prosthesis particularly adapted for use as a knee joint, wherein the prosthesis is designed for enhanced noncemented attachment to patient bone tissue and further wherein the prosthesis is configured to withstand high loading and stress thereby providing a prolonged service life. The present invention fulfills these needs and provides further related advantages.